1. Field of the Invention
The present invention relates to a vacuum-adsorbing apparatus of a semiconductor device fabrication facility. More particularly, the present invention relates to a vacuum-adsorbing apparatus of a robot arm which transfers reticles or semiconductor wafers to and from photolithographic equipment in a semiconductor device fabrication facility.
2. Description of the Related Art
Generally speaking, the fabricating of semiconductor devices involves subjecting a wafer to an array of processes such as cleaning, diffusion, photolithographic, etching, and ion-injection processes. The photolithographic process must be carried out before the etching or ion-injection processes. In photolithography, an image from a reticle is transferred onto the wafer using a photoresist. Photolithography can be roughly divided into four steps, namely photoresist deposition, alignment and exposure, development, and inspection.
To begin these steps, both the wafer and a reticle must be set at precise positions. In this respect, the wafer is moved from a carrier to a wafer stage by a wafer loader. On the other hand, the reticle is moved from a case to a reticle stage by a reticle loader.
Recently, wafer loaders and reticle loaders have employed vacuum-adsorption as a means to secure the wafers and reticles to a robot arm while at the same time preventing the wafers and reticles from being broken or damaged, e.g. from being scratched. The conventional wafer loader or reticle loader has a vacuum line opening into a mounting plate to which the wafer or reticle is adhered under the vacuum established in the line. In addition, a vacuum sensor is provided in the vacuum line for sensing the state of the vacuum, which information is used to adhere or detach the object (wafer or reticle) to or from the mounting plate.
FIGS. 1 and 2 show the conventional vacuum sensor. The vacuum sensor 10 has a nozzle 12 connected to the vacuum line (not shown), and a screw 14 for controlling the distance between inner contacts 18, 20 of a switch. More specifically, the vacuum sensor 10 is turned on and off electrically by a diaphragm 16 moved by the air passing through the nozzle 12. If the air is drawn out of the sensor via the nozzle 12, the diaphragm 16 pushes a movable iron plate spring 18 into contact with a fixed iron plate 20. On the other hand, if air is led back into the sensor via the nozzle 12, the diaphragm 16 is relaxed, and the iron plate spring 18 springs back to its original position so as to be detached from the fixed iron plate 20.
The vacuum sensor outputs an electric sensing signal indicative of the existence/non-existence of a vacuum according to the state (contact/non-contact) between the fixed iron plate 20 and the movable iron plate spring 18. In addition, the fixed iron plate 20 can be re-positioned by the screw 14 to adjust the spacing between the fixed iron plate 20 and the movable iron plate spring 18, and hence, the sensitivity of the sensor.
However, because the vacuum sensor comprises mechanical contacts, the sensitivity of the sensor degrades over time. In fact, such a sensor is prone to failures or malfunctions, whereby an operator can not tell whether the wafer or reticle is adhered sufficiently, or at all, to the robot arm. When such a sensing error occurs, the wafer or reticle can be shook or can even fall from the robot arm and become scratched or broken.